1. Field of the Invention
The present invention relates to a control system for an industrial robot.
2. Description of the Prior Art
A conventional motor control circuit which drives an industrial robot at r, .theta. and z directions (r is an absolute value, .theta. is an argument in polar coordinates and z direction is the perpendicular direction to the r, .theta. plane), and performs that the circuit receives a position command pulse, gains a difference of the pulse numbers between the position command pulse and a position feedback signal, the difference is set on an error register, the contents of the error register is converted to an analog value through digital-analog (DA) converter, and the motor is driven through a speed control device according to the analog value. In this system, since the value of the error register directly applies to the DA converter, the control by which the increase of the motor driving signal pulse is controlled cannot be accomplished corresponding to the value indicated on the error register. Particularly there is a problem that the positioning error is increased when the motor stops the rotation.
Besides, a system in which a position gain multiplier inserted between the error register and the DA converter, is utilized, however, the system has only a fixed constant characteristic between the indicated value of the error register and the gain of the position gain multiplier, namely, the system controls the output of the DA converter along the straight lines corresponding to the error quantity being set on the error register, therefore, enough satisfaction regarding the error of the stopping position cannot always be obtained in the above-mentioned case.
The present invention is proposed in order to solve the above described problem in the conventional art.